Band saw machines include vertical band saw machines and horizontal band saw machines. In order to facilitate understanding, schematic descriptions will be provided for an overall configuration of a horizontal band saw machine as an example of the band saw machines. As conceptually and schematically shown in FIG. 1, a horizontal band saw machine 1 includes a base 3. A vise device 5 to which a workpiece W to be cut off can be fixed is mounted on this base 3. The vise device 5 has a configuration including: a fixed vise jaw 9A which is fixed to a vise head 7 for supporting the workpiece W; and a movable vise jaw 9b. The fixed vise jaw 9A and the movable vise jaw 9b are set opposite to each other. The vise device 5 includes a hydraulic cylinder 11 for operating the movable vise jaw 9B. A saw blade housing 15 including a band saw blade 13 for cutting off the workpiece W is movably provided above the base 3. The saw blade housing 15 thus provided is capable of moving in such directions as to make the saw blade housing 15 relatively move close to/away from the workpiece W. In other words, the saw blade housing 15 moves in upward and downward directions in the illustrated example.
In other words, in this example, a lifting member 19 included in the saw blade housing 15 in an integrated manner is guided by a guide post 17 mounted upright on the base 3 in a way that the lifting member 19 is movable upward and downward. In addition, a lifting hydraulic cylinder 21 as an example of a cutting actuator is provided in such directions as to make the saw blade housing 15 relatively move close to/away from the workpiece W. In other words, the saw blade housing 15 moves in upward and downward directions in the illustrated example. Furthermore, for the purpose of detecting a position indicating where the band saw blade 13 cuts into the workpiece W, the horizontal band saw machine 1 is provided with a cutting position detector 23 for detecting the position indicating where the band saw blade 13 cuts into the workpiece W through detecting a position indicating how far upward and downward the saw blade housing 15 moves.
The cutting position detector 23 may have a configuration including a vertical linear scale provided on the guide post 17 and a detection head, for example, or may have a configuration in which a rotary encoder is rotated by a pinion engaged with a rack. In a mode in which the saw blade housing 15 swings vertically, the rotary encoder may be provided on a hinge in the saw blade housing. Thus, various configurations can be used.
The saw blade housing 15 has a configuration that includes wheel housings 27A and 27B on the left and right sides of a beam member 25 long in the left-and-right direction in the drawing. The saw blade housing 15 has a configuration in which a driving wheel 29 is rotatably provided in one of the wheel housings, 27A, whereas a driven wheel 31 is rotatably provided in the other wheel housing 27B. In addition, the saw blade housing 15 has a configuration in which the band saw blade 13 is suspended between the driving wheel 29 and the driven wheel 31. Band saw blade guides 33 for guiding and holding the band saw blade 13 with the cutting edge of the band saw blade 13 being directed to the workpiece W are provided between both the wheel housings 27A and 27B.
The horizontal band saw machine 1 of the foregoing type is publicly known. For this reason, the descriptions for how the above-described configurations operate the band saw machine are omitted.
With the above-described configurations, a motor 37 installed in the wheel housing 27A is rotationally driven, the driving wheel 29 is thus rotated, and the saw blade housing 15 is caused to descend with the band saw blade 13 being rotationally running, under control of a controller 35 such as a CNC. Thereby, the workpiece W is cut off by the band saw blade 13.
The band saw blade 13 has a configuration which has a large number of saw teeth, arranged in intervals that vary depending on the necessity, on one side of the band saw blade 13 in the width direction. The saw teeth cut into the workpiece W, and thus the cutting-off processing of the workpiece is accomplished. In this respect, cutting resistance working on each saw tooth is not equal, for example, depending on its abrasion. Variation in cutting resistances is highly likely to cause the band saw blade 13 to oscillate (longitudinal or compressional oscillation) in a direction in which the band saw blade 13 runs (in a direction in which a main component force is produced) (hereinafter referred to as a “main-component-force direction”). In some cases, this oscillation develops into a chatter oscillation accompanying abnormal noises.
For the purpose of restraining noises which occur due to the chatter oscillation, various countermeasures have been heretofore adopted. Such countermeasures include: increasing mechanical rigidity; interposing the band saw blade between oscillation isolating rollers; and covering the band saw blade so as to prevent noises from leaking. Nevertheless, configurations of a conventional type impose limitation on the restraining of the chatter oscillation which occurs due to the longitudinal oscillation.
As a reference, Japanese Patent Application, Laid-Open No. 2004-284006 (Patent Document 1) is a preceding example which has some bearings on the present invention.
In the case of a configuration as recited in Patent Document 1, when the workpiece is cut off, pulses are applied to a control motor for rotationally driving the band saw blade, and thus the running speed of the band saw blade is oscillated. The cutting off of the workpiece by oscillating the running speed of the band saw blade is equivalent to vibration cutting using the band saw blade. A workpiece is cut off better by the cutting-off method with this configuration than by a cutting-off method of the conventional type using a regular band saw machine, and concurrently noises are restrained (checked) from occurring.
In other words, the effect of restraining noises from occurring while the workpiece is being cut off is enhanced to some extent. Nevertheless, it is still expected that a chatter oscillation which occurs to the band saw blade due to its longitudinal oscillation (its oscillation occurring in the main-component-force direction) will be effectively restrained (checked).
The present invention has been made for the purpose of solving the foregoing problem. An object of the present invention is to provide a method of cutting off a workpiece, which method is capable of restraining (checking) of a band saw blade from chattering, and a band saw machine used for the cutting-off method.